Comment by lambda | Hacker News Reader

Comment by lambda | Hacker News Reader

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Nope. We're pretty much limited by battery technology on that front; you need bigger batteries to provide more power, but those bigger batteries mean more weight, which means more power needed just to stay aloft. For a battery powered multicopter, I think an hour or so is about the highest you can get (I don't think I've seen any that claim over 40 minutes), and as you point out, most drones are closer to the 15 to 20 minute range.

Of course, there are other designs like fixed wing planes which can be a bit more efficient though more complicated to navigate in confined spaces and without the ability to hover, and you can use internal combustion engines which can get you much longer flight times due to the higher energy density of their power source. But I don't think you're going to find any of the affordable, battery powered multicopters that get you anything over an hour (and even then, I would set my expectations at more like a half-hour for anything affordable in realistic conditions).

Wireless power transmission via laser:

> Stalker is a small, silent UAS used by Special Operations Forces since 2006 to perform intelligence, surveillance and reconnaissance missions. In a recent wind tunnel test, the UAS demonstrated 48 hours of continuous flight powered by this innovative laser system.

> Demonstrated net positive power to Stalker in flight, at ranges up to 600 meters.

> The beam director tracked the receiver for long periods, with centimeter accuracy at 500 meters, despite turbulence and aircraft maneuvers.

http://lasermotive.com/products/uav-power-links/

Note they first successfully demonstrated this outdoors 3 years ago: http://www.lockheedmartin.com/us/news/press-releases/2012/au...

This is genuinely awesome and I'm excited to see it's applications in future products.

HOWEVER: I don't think it's ready for 'consumer grade' things just yet. It's one thing to have it in a controlled wind-tunnel for 48 hours, it's completely different than having it outside and in variable wind, dirt, dust, other objects, etc.

Honestly, I can't imagine my luddite brother or father wrapping their minds around this just yet: "So, I point the laser at this? Why can't I just use a flashlight? Can I use the laser to charge my phone?"

Yes, another approach is to not have to carry all of the energy with you. Solar charging is another possibility.

I don't know that the energy density of solar cells work for their weight. Electric motors require a pretty high current. Even if you are supplementing another power source, I think you'll still be losing more than you are gaining for that application. You are probably fine with fixed wing, but multicopter designs will draw significantly more power.

I'd assume he's referring to having solar charging stations at the way-points.

How stealthy is this thing if it has a giant laser pointed at it the whole time?

Beam coherence and illumination aren't issues at the distance and power levels used.

We have this thing called infrared. The military is quite fond of it already for targeting lasers.

Huh.

That's actually really interesting.

I have this vision of a large mother UAV with long loiter times that can laser target micro UAVs at much lower altitudes.

Definitely feasible if your mothership is a dirigible using gas turbines to power itself, using laser spotbeams to target drones below for providing remote power.

I wonder why more remote-operated drones like this aren't being designed with gasoline motors rather than electric. I remember flying all kinds of tiny gas-powered RC planes as a kid, and it's not obvious to me that the benefits of electric out-weigh the multiple-orders-of-magnitude reduction in flight time. In fact, what are the principal advantages of electric UAVs over gas-powered?

Price and safety, I would bet.

Most quadcopters aren't gas-powered because they rely on rapidly adjusting the speed of brushless motors attached to fixed-pitch props to control their attitude.

A few hobbyists have built gas quads with variable-pitch rotors, but the amount of mechanical complexity and hassle involved makes a similar nitro-powered single-rotor helicopter more appealing for most hobby applications (stunt flying etc).

As more novel designs that don't rely on precise motor speed control (for example, this one) come into play, I think gas motors will make a minor resurgence as people rediscover the energy density (and therefore flight time) they can achieve.

However, for most hobbyists, electric just makes more sense. It's usually quieter, works indoors, is generally a lot less of a pain in the ass to deal with (no need for starters, glow plugs, choke, adjusting mixture, engine maintenance, etc.), and is usually less heavily regulated.

Why not hybrid? Have an onboard gas generator to recharge the batteries. As soon as the gas runs out, the drone has X min of battery flight time left to get back to solid ground. No need for mechanical complexity.

Hell, you could have a small buffer ultra capacitor or battery providing the motors with electricity while a gas engine at constant RPM recharges it. The whole system would have to have a very high conversion efficiency though...

There's an MIT spinoff called Top Flight that was working on a hybrid quadcopter, IIRC. I think the main reason you don't see them in the hobbyist space is size floor (you need a pretty big machine to make the weight overhead of the motor, generator, and charge circuitry work out) and money.

Gas engines could be coupled with one or several CVT transmissions?

I think you could just use the simplest form of CVT: a variable-diameter pulley under each rotor. You'd still pay a pretty big cost in terms of mechanical complexity, though, which makes the swashplate system more appealing as offers a lot of additional advantages in terms of thrust vectoring.

For multirotors it's just very difficult and impractical to power them with gasoline engines. If you were to build a gas powered multirotor, you'd have to have a central engine connected to each motor by means of some complicated mechanical linkage. This would also mean you could no longer control the speeds of the motors individually, so you'd have to achieve lateral movement by pitching the propellers, like on a helicopter. All these things mean that it simply doesn't make sense to build a non-electric multirotor, it'd be massively expensive and inefficient you'd be better off going back to a helicopter.

In terms of fixed wing drones, the benefit of electric over gas is mainly ease of use I believe. It's a lot simpler for someone to charge a battery and just plug it in than it is for them to fill up canisters, refuel the engine and cope with the complexities of tweaking and starting an engine. That extra effort and learning curve isn't worth it for the slightly longer slight time.

For aerial mapping the go-to option is normally fixed wing drones, they can easily achieve 30-40 minutes of flight time and this is normally enough for those kind of applications.

For a coaxial, cyclic controlled UAV like this you could convert to using a fixed RPM gas engine though.

Control and cost.

PWM motors can control their rotation very precisely unlike IC motors. That is one reason you see multicopter designs nowadays. You can quickly alter the torque. I didn't see how this design alters pitch or roll, but I know there were some coaxial experimental designs that can alter the torque in a single rotation to affect those axis. That is simply not possible with something powered by burning fuel. It might be possible to have a mixed system, using an internal combustion engine for primary lift and electronically controlled steering, but that would be a more complex system and the benefit isn't abundantly clear.

Size, noise, maintenance, predictability, simplicity, cost. Haven't seen a power/weight trade study of batteries vs engine+generator+fuel, but it may be closer than you think. There's a lot involved in a ICE power plant, and even if it did win, it'd have to be a pretty big machine compared to your average multirotor due to minimum scale on gasoline engine components.

There might be a market for large endurance multirotors, but apparently it's not obviously attractive.

The solution is to allow the drone to hot-swap the battery. You would put a bunch of batteries along the drone's planned flight path and it would automatically detect these batteries and replace its own emptying battery with the one placed on the ground.

Potentially, if autonomous drones really take off, there could be a countrywide system of solar-powered charging stations that would supply drones with standardized batteries. Such infrastructure would be almost completely self-sufficient and allow drones to fly any distance.

In fact, this model also works for electric cars, manned or unmanned. There's no reason why Tesla Supercharger stations cannot provide a fully charged battery to swap into your car. Of course you'd have to deposit your own battery first so that you cannot get a battery for free.

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